In wireless communication systems, an electronic device (ED), such as a user equipment (UE), wirelessly communicates with a Transmission and Receive Point (TRP), termed “base station”, to send data to the ED and/or receive data from the ED. A wireless communication from an ED to a base station is referred to as an uplink communication. A wireless communication from a base station to an ED is referred to as a downlink communication.
Resources are required to perform uplink and downlink communications. For example, an ED may wirelessly transmit data to a base station in an uplink transmission at a particular frequency and during a particular time slot. The frequency and time slot used is an example of a physical communication resource.
In an LTE grant-based transmission, the required transmission control parameters are typically communicated via a Physical Uplink Control Channel (PUCCH) and/or Physical Downlink Control Channel (PDCCH). The base station is aware of the identity of the ED sending the uplink transmission using the granted uplink resources, because the base station specifically granted those uplink resources to that ED. In a grant-free transmission, different EDs may send uplink transmissions using uplink resources shared by the EDs, without specifically requesting use of the resources and without specifically being granted the resources by the base station. One advantage of grant-free transmission is low latency resulting from not having to request and receive a grant for an allocated time slot from the base station. Furthermore, in a grant-free transmission, the scheduling overhead may be reduced. However, the base station does not have information which ED, if any, is sending a grant-free uplink transmission at a particular moment of time, which may require blind detection of grant-free transmissions received at the base station. In other words, the base station is required to determine which ED is transmitting. Therefore, the BS can use the combination of uplink reference symbols (RS) and occupied time-frequency resources to identify a grant-free ED as well as the transport block being received from that grant-free ED.
Some modes of communication may enable communications with an ED over an unlicensed spectrum band, or over different spectrum bands (e.g., an unlicensed spectrum band and/or a licensed spectrum band) of a wireless network. Given the scarcity and expense of bandwidth in the licensed spectrum, exploiting the vast and free-of-charge unlicensed spectrum to offload at least some communication traffic is an approach that has garnered interest from mobile broadband (MBB) network operators. For example, in some cases uplink transmissions may be transmitted over an unlicensed spectrum band. Accordingly, efficient and fair mechanisms for grant-free uplink transmissions in the unlicensed spectrum may be desirable.